Curved preform and method of making thereof

ABSTRACT

Disclosed is an apparatus and method for forming three-dimensional woven preforms that can be curved and have continuous fibers in the direction of curvature. Also disclosed are woven preforms formed thereby.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage entry under 35 U.S.C. § 371 ofInternational Application Number PCT/US2019/044582 filed on Aug. 1,2019, published on Feb. 6, 2020 under publication number WO 2020/028613A1, which claims the benefit of priority of U.S. Provisional ApplicationSer. No. 62/713,206 filed Aug. 1, 2018, which are hereby incorporated byreference in their entireties.

BACKGROUND 1. Field

This disclosure relates to woven preforms and particularly relates towoven preforms used in reinforced composite materials. Moreparticularly, the present invention relates to woven preforms that arecurved with continuous fiber reinforcement.

2. Related Art

The use of reinforced composite materials to produce structuralcomponents is now widespread, particularly in applications where theirdesirable characteristics of light weight, high strength, toughness,thermal resistance, and ability to being formed and shaped can be usedto great advantage. Such components are used, for example, inaeronautical, aerospace, satellite, high performance recreationalproducts, and other applications.

Typically, such components consist of reinforcement materials embeddedin matrix materials. The reinforcement component may be made frommaterials such as glass, carbon, ceramic, aramid, polyester and/or othermaterials that exhibit desired physical, thermal, chemical and/or otherproperties, chief among which is strength against stress failure.

Through the use of such reinforcement materials, which ultimately becomea constituent element of the completed component, the desirablecharacteristics of the reinforcement materials, such as high strength,are imparted to the completed composite component. The typicalconstituent reinforcement materials may be woven, knitted or otherwiseoriented into desired configurations and shapes for reinforcementpreforms. Usually particular attention is paid to ensure the optimumutilization of the properties for which the constituent reinforcingmaterials have been selected.

After the desired reinforcement preform has been constructed, matrixmaterial may be introduced into the preform so the reinforcement preformbecomes encased in the matrix material and matrix material fills theinterstitial areas between the constituent elements of the reinforcementpreform. The reinforcement preform combined with matrix material canform desired finished components or to produce working stock for theultimate production of finished components.

The matrix material may be any of a wide variety of materials, such asepoxy, polyester, vinyl-ester, ceramic, carbon and/or other materials,which also exhibit desired physical, thermal, chemical, and/or otherproperties. The materials chosen for use as the matrix may or may not bethe same as that of the reinforcement preform and may or may not havecomparable physical, chemical, thermal and/or other properties.Typically, however, they will not be of the same materials or havecomparable physical, chemical, thermal, or other properties, because ausual objective sought in using composites in the first place is toachieve a combination of characteristics in the finished product that isnot attainable through the use of one constituent material alone. Socombined, the reinforcement preform and the matrix material may then becured and stabilized in the same operation by thermosetting or otherknown methods, and then subjected to other operations toward producingthe desired component. It is significant to note at this point thatafter being so cured, the then solidified masses of the matrix materialnormally are very strongly adhered to the reinforcing material (e.g.,the reinforcement preform).

A common method of producing a woven preform is to weave a twodimensional (“2D”) structure and fold it into a three dimensional (“3D”)shape. A benefit of folded preforms is the strength of the joint betweenthe panel to be reinforced and the reinforcing panel. As they are woventogether, the panels share reinforcing material and in the finalcomposite, matrix material, creating a unitary construction. Thejuncture between the integrally woven reinforcement flange or leg andthe parent material or base is no longer the weak link, relying solelyupon the strength of the adhesive for the strength of the joint, as inthe prior-art reinforcements. Instead, the fibers of the preformintegrally weave the legs and the base together.

Frequently, however, complex shapes, such as curves, requirereinforcement. Folded T- or Pi-shaped and other preform reinforcementshaving a flange base with one or more upstanding legs require darting ofthe legs in order to accommodate a curved surface. As the flangematerial of a folded preform assumes a curved shape, the length of thecurved surface necessarily varies from the inside of the curvature tothe outside of the legs. The arc length of outside of the curvature, thesurface with the larger radius when curved, increases, while on theinside of the curvature, the arc length decreases. The legs of typicalfolded preforms cannot change length as required to accommodate a curvedsurface. To accommodate a curved surface, the legs must be darted. Thatis, the legs must be cut or have discontinuous fibers in order to allowthe leg to conform to the changed arc length.

Typically, the cut is along the localized radius of curvature, butother, non-radial cuts may also be used to accommodate the change inlength. To allow for the decreased length on the inside of a curvedpreform, the leg is cut and the cut edges allowed to overlap, or theexcess material is removed. Similarly, to accommodate the increasedlength on the outside of the curvature, the leg is cut, resulting in atriangular gap between cut edges of the leg. In either configuration,the darting breaks the continuity of the reinforcing fibers in each leg.Darting the legs of a 3D T- or Pi-preform can degrade the load carryingcapabilities of the preform, because darting involved cutting the fibersthat provide the primary load path around the curve.

SUMMARY OF THE DISCLOSURE

A method of forming a curved preform includes applying at least one setof mating clamps to fibers of a preform fabric advancing from a loom,the at least one pair of mating clamps capturing at least a portion ofthe preform fabric there between. The at least one set of clamps havinga geometry to increase a length of fibers by pulling at least some ofthe fibers advancing from the loom. The preform fabric is shaped into acurve. And the fibers are continuous along a length of the fabric. Insome embodiments, the length of the fibers is greater at an outside ofthe curve than at an inside of the curve. In other embodiments, thelength of the fibers is shorter at an outside of the curve than at aninside of the curve.

In one embodiment, each set of mating clamps is a pair of clamps. Inanother embodiment, each set of mating clamps is at least three clamps.The mating clamps may include an upper clamp portion and a lower clampportion. In certain embodiments, the lower clamp portion comprises atleast two mating parts.

In certain embodiments, there are at least two sets of mating clampsapplied to the preform fabric. A force is applied to each set of matingclamps to compress the preform fabric there between. Adjacent matingclamps may be mated to one another. The two or more sets of matingclamps can be disposed in separate locations of the preform fabric toincrease the length of the fibers in each of the separate locations butnot in other locations.

In other embodiments, described herein are curved woven preforms, forexample, a curved woven preform comprising a plurality of weft fibersand a plurality of warp fibers interwoven with the plurality of weftfibers to form a base of the preform, wherein the base of the preform iscurved with the warp fibers continuous across the length of the preformand some of the warp fibers are longer than other warp fibers.

In certain embodiments, the curvature of the woven preform is convex,the length of the warp fibers being greater towards an outside of thecurve of the preform than towards an inside of the curve of the preform.In a further embodiment, the preform comprises at least one legintegrally woven with the base and curved along a length of the base,wherein warp fibers forming the at least one leg are greater towards anoutside curve of the at least one leg than towards an inside curve ofthe at least one leg.

In other embodiments, the curvature of the woven preform is concave, thelength of the warp fibers being shorter towards an outside of the curveof the preform than towards an inside of the curve of the preform. In afurther embodiment, the preform comprises at least one leg integrallywoven with the base and curved along a length of the base, wherein warpfibers forming the at least one leg are shorter towards an outside curveof the at least one leg than towards an inside curve of the at least oneleg.

The instant invention also relates to clamps, such as an upper clampmateable with a lower clamp, wherein the upper clamp has a complementaryshape to mate with the lower clamp and configured to receive a fabrictherebetween. In another embodiment, the invention relates to an upperclamp having a blade portion and a lower clamp separable and mateablewith the upper portion, the lower clamp having a lower clamp first partand a lower clamp second part, wherein the lower clamp first and secondparts have a gap therebetween such that the blade portion of the upperclamp enters into the gap when the upper and lower clamps are matedtogether.

In yet other embodiments, the invention relates to a shaping clampsystem comprising two or more clamps, each clamp having an upper clampportion and a lower clamp portion and an integral connecting portion,wherein the two or more clamps are connectable to one another by theconnecting portion and configured to receive a fabric therebetween. Incertain embodiments, the invention relates to a shaping clamp systemcomprising two or more clamps, each clamp having an upper clamp portionwith a blade portion and a lower clamp portion, each clamp including anintegral connecting portion, wherein each lower clamp is separable andmateable with a respective upper clamp, the lower clamp having a lowerclamp first part and a lower clamp second part with a gap therebetweento receive the blade portion when the upper clamp and lower clamp aremated together, wherein the two or more clamps are connectable to oneanother by the connecting portion and configured to receive a fabrictherebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, are incorporated in and constitute apart of this specification. The drawings presented herein illustratedifferent embodiments of the invention and together with the descriptionserve to explain the principles of the invention. In the drawings:

FIGS. 1A-1C illustrate an example of a T-preform as woven and foldedinto a final shape.

FIGS. 2A-2B illustrate an example of a curved T-preform.

FIG. 3 illustrates an example of a clamp geometry to increase the lengthof fibers in the tip of a preform as compared with the root of thepreform.

FIGS. 4A-4B illustrate a fabric having lengthened fibers between thefabric width edges.

FIG. 5 illustrates application of pairs of mating clamps to a preformfabric to increase the length of fibers.

FIG. 6 illustrates another embodiment of a clamp for lengthening fibersof a preform fabric.

FIGS. 7A-7B illustrate application of the clamp of FIG. 6.

FIGS. 8A-8E illustrate examples of preforms having complex geometriesthat may be formed.

FIG. 9 illustrates an example of an O preform that may be formed.

FIG. 10 illustrates an example of a clamp design according to theinstant invention.

DETAILED DESCRIPTION

Terms “comprising” and “comprises” in this disclosure can mean“including” and “includes” or can have the meaning commonly given to theterm “comprising” or “comprises” in U.S. Patent Law. Terms “consistingessentially of” or “consists essentially of” if used in the claims havethe meaning ascribed to them in U.S. Patent Law. Other aspects of theinvention are described in or are obvious from (and within the ambit ofthe invention) the following disclosure.

The terms “threads”, “fibers”, “tows”, and “yarns” are usedinterchangeably in the following description. “Threads”, “fibers”,“tows”, and “yarns” as used herein can refer to monofilaments,multifilament yarns, twisted yarns, multifilament tows, textured yarns,braided tows, coated yarns, bicomponent yarns, as well as yarns madefrom stretch broken fibers of any materials known to those ordinarilyskilled in the art. Yarns can be made of carbon, nylon, rayon,fiberglass, cotton, ceramic, aramid, polyester, metal, polyethyleneglass, and/or other materials that exhibit desired physical, thermal,chemical or other properties.

The term “folded” is broadly used herein to mean “forming,” whichincludes unfolding, bending, and other such terms for manipulating theshape of a fabric.

For a better understanding of the invention, its advantages and objectsattained by its uses, reference is made to the accompanying descriptivematter in which non-limiting embodiments of the invention areillustrated in the accompanying drawings and in which correspondingcomponents are identified by the same reference numerals.

Disclosed is a method for creating curved preforms of continuous fiberon a conventional straight loom take-up. Machine woven fabrics arecreated using a loom that includes a weaving mechanism coupled with amethod for advancing and collecting the finished fabric. “Straighttake-up” means the fabric is collected in the warp or machine direction(MD) in short lengths adapted for weaving discrete preforms.

Typical shapes woven with the straight take-up include Pi-shaped orT-shaped preforms used as structural reinforcement members in a varietyof applications. These shapes being made of continuous fiber in both thewarp and weft directions can be difficult to form into a geometry orcurved shape in the warp or take-up direction.

As an example, FIGS. 1A-1C illustrate a simplified version of forming aT-preform from T-preform fabric 100. Warp and weft fibers are interwovenin a loom 106, illustrated by the dotted lines. As the T-preform fabricis woven, the fabric advances in the direction A towards a take-up roll(not shown) for receiving the completed fabric. The portion of thefabric that has already been formed but not yet rolled up on the take-uproll is called the “fell” 108.

The T-preform fabric includes base portions 102 a, 102 b and leg portion104. A root 110 of leg portion 104 may be interwoven with base portions102 a, 102 b. Base portions 102 a, 102 b are not interwoven at theirintersection 114 and the remainder of the leg portion 104 is notinterwoven with the base portions other than at their intersection 110.The T-preform fabric 100 is woven and advances toward and onto thetake-up roll. Once a desired length L of the T-preform fabric is woven,the fabric may be removed from the loom. Base portions 102 a, 102 b, andleg portion 104 can be folded to form T-preform 120.

Other preform shapes including, but not limited to, Pi, H, O, and I canbe woven and folded into their final form as known to those of ordinaryskill. Any of the preforms can be impregnated with a matrix material toform a composite.

FIG. 2A illustrates an example of a curved preform. For purposes ofdiscussion, the curve illustrated in FIG. 2A and other figures isreferred to as being “convex.” Accordingly, the example is of a convexT-shaped preform but other preform shapes including, but not limited to,Pi, H, O and I are contemplated. Similar to the fabric in FIG. 1, theT-preform fabric includes base portions 202 a, 202 b and leg portion204. Base portions 202 a, 202 b and leg portion 204 are folded to formT-preform 220.

Base portions 202 a, 202 b and leg portion 204 are woven from warpfibers 222. As shown in FIG. 2B, the length L2 of warp fibers 222 in thewarp direction are shorter towards the inside or root 226 of the curvedT-preform than towards the outside or tip 224 of the curved T-preform.Accordingly, in order to curve a preform woven as in FIG. 1, the fiberlength in the warp direction must be greater at the tip of the curvedpreform than at the root of the curved preform.

While curved preforms are known in the art, these prior-art preformsrequired cutting of fibers or making the length from discontinuous shortfibers, such as stretch broken fibers, to enable the preform to bestretched or curved to provide additional length of the preform towardsthe outside of the curvature as compared with towards the inside of thecurvature. There is a weakening, a loss of strength, of the preform dueto the cutting and/or discontinuity of the fibers in providing theadditional length.

In contrast, the present disclosure provides preforms and a process forweaving preforms with additional length of fibers so the finishedstructure can be curved and have continuous fiber reinforcement in thedirection of the curvature. Continuous fibers provide greater preformstrength than discontinuous fibers. “Continuous fibers” are fibershaving no breaks along the entire length of the fabric. In embodimentsof the present disclosure, the fibers of the fabric are continuous inthe direction of curvature of the preform and can have varying lengthsacross the width of the fabric. The varying lengths across the preformfabric width enable forming a curved portion in the length of the fabricwithout cutting the fibers or having the fibers discontinuous to formthe curved portion.

For the purposes of this disclosure, the direction of curvature of thepreform will be assumed to be along the warp or machine direction (MD)of the fabric. However, it is contemplated that the disclosed techniquemay be used to effect curvature of the fabric in the weft orcross-machine direction (CD) alone or in combination with the warpdirection.

To create this curvature, according to an embodiment of the presentdisclosure, the length of the fibers in upright leg 204 is made longertowards the outside tip 224 of the preform upright leg than the insideroot 226 of the preform leg by applying one or more clamps to the fabricas the fabric comes off of the loom. The clamps may be applied in thefell of the doth. The shape of the clamps is designed to draw additionalfiber length into the preform to accommodate an increase in length ofthe fibers to enable curvature of the preform when the preform is formedto the desired shape.

In embodiments of the instant invention, each clamp incrementallyincreases the length of the warp fibers coming off the loom. In theclamp depicted in FIG. 10, for example, to accommodate the longer radiusof the outside of a preform curvature (Ro) versus the shorter radius ofthe inside of the curvature (Ri), the clamp is designed such that aseach clamp segment is applied to the warp fibers coming off the loom,the resulting length of the warp fiber on the inside (Wi) of the preformcurvature is shorter than the warp fiber on the outside (Wo) of thepreform curvature. The resulting difference in length of the fibers, Woand Wi, is shown.

It is contemplated that the preform fabric can be made concave asillustrated in the examples of FIGS. 8C, 8D, and 8E. In embodiments ofconcave preform fabrics such as FIG. 8D having base portions 802 a, 802b, the lengths of the warp fibers forming the upright legs 804 would beopposite to that of the convex preform fabric. That is, the length ofthe fibers in upright legs 804 are shorter towards the outside tip 824of the preform upright leg than towards the inside root 826 of thepreform leg. Those of ordinary skill in the art will appreciate thegeneral understanding that the geometry of the final preform shapedetermines the necessary length of fibers across the preform length toenable forming the required curvature. Altering of the length of thefibers so that they are continuous across the length of the fabricdistinguishes forming preform fabrics according to the presentdisclosure from the discontinuous fibers across the length of prior-artcurved preforms.

FIG. 3 illustrates an example of a clamp element 300. The clamp 300 isapplied to the preform fabric exiting the loom. The clamp is oriented onthe preform fabric so that a clamp root end 326 is applied to the rootend of an upright leg and a clamp tip end 324 is applied to the tip endof the upright leg. For a convex curvature as in FIGS. 1 and 2, theclamp root end is straight, which does not increase the length of thefibers because the root end of the T-preform upright leg has theshortest length of fibers in the curved preform. The clamp tip end has ageometry or shape to lengthen the preform fabric fibers of a convexcurvature. That is, the geometry of the clamp causes added fiber take-uplength to be drawn from the loom to traverse across towards the clamptip end than towards the clamp root end. The geometry is morepronounced—causing greater fiber take-up length to be drawn from theloom—at the clamp tip end because the tip end of a convex preform withan upright leg(s) has the longest fibers in the curved preform. Thegeometry of the clamp is reduced towards the clamp root end as thelength of the fibers are shorter towards the root of the curved preform.In this way the fibers are longest at the tip of the curved preformfabric upright leg and shortest at the root. Of course, the geometry ofthe clamp is reversed with respect to the upright leg of a preform withconcave curvature.

The clamps are typically assembled on the preform fabric in sets. Eachset of clamps includes two or more clamps having mating geometries. Theclamping action of sandwiching the preform fabric between the set ofclamps draws additional fiber take-up length through the loom. The clampset geometries are tapered such that the take-up length increases fromthe root (inside curve of the preform) to the tip of an upright leg(s)(outside curve of the preform) for a preform with convex curvature(reversed clamp geometry for a preform with concave curvature). Theincrease in length of the fibers can enable forming of the preformfabric into the curved preform of FIG. 2 with continuous lengths offibers throughout the curved preform. The curvature of the preform isachieved with continuous lengths of fibers and not weakened by cuttingfibers or shortened fibers, such as stretch broken fibers.

The geometry of a clamp shown in FIG. 3 is for illustrative purposesonly. Design considerations will determine the particular geometryselected for the clamps. Moreover, the geometry of the clamps can bevaried over the length of a preform to provide for alternative contoursor curvatures of the preform fabric over the length of the preform.

FIG. 4A illustrates a fabric where the clamp geometry has been arrangedto provide a lengthening of the fibers anywhere along the width of thefabric. That is, the fibers may be lengthened between the width edges ofthe fabric to cause a curvature across the width of the fabric. In oneembodiment, the clamp sets are arranged to cause a lengthening of thefibers toward the center of the fabric. In one embodiment, the preformfabric can be cut in the middle of the warp direction to create twocurved preforms with continuous fiber along the length of curvature. Asshown in FIG. 4B, in this embodiment, the curvature is arranged in theplane of the preform fabric. It is contemplated that clamp geometrycould also be made to cause a lengthening of fibers in a multilayerfabric. Some of the layers can be folded into one or more upstandinglegs from the plane or base of the preform fabric that follow thecurvature of the plane of the preform fabric and shown in FIG. 2.

FIG. 5 illustrates an embodiment where the set of clamps is a pair ofmating clamps 502 a, 502 b assembled on preform fabric 504 as the fabricexits the loom 506. These clamps may be held in place throughout theweaving process by a force F applied to the mating clamps to press thepreform fabric between the clamps and vary the length of continuousfibers along the length of the preform. The force holding the clamppairs together may be achieved in any manner known to those of ordinaryskill including, but not limited to, screws and nuts, springs, etc. Inone embodiment, adjacent clamp pairs, such as 508, 510, can be assembledto one another.

FIG. 6 illustrates an embodiment where a set of clamps 600 is arrangedto intersect to lengthen the fibers when applied to a preform fabric.The set of clamps 600 includes an upper clamp 602 having a blade portion608. A lower clamp 610 has portions 604, 606 having a gap 612therebetween to receive blade portion 608. Lower clamp 610 may be asingle piece or attached separate pieces. If separate pieces, clamp set600 may be considered to have an upper clamp 602 and lower clamps 604,606. An advantage of separate pieces for clamp set 600 is that each ofthe pieces may be mechanically the same to reduce cost of manufacturingand stocking the parts. Also, the gap 612 between lower clamps 604, 606may be varied to accommodate differing preform fabric thicknesses.

FIGS. 7A-7B illustrate the set of clamps 600 being brought together. InFIG. 7A the upper clamp 602 is arranged on top of the preform fabric(not shown for clarity) and lower clamp 610 is arranged beneath thepreform fabric. The upper and lower clamps are separated by a distance702 so that blade 608 of the upper clamp does not enter the gap 612 inthe lower clamp.

The blade portion for a convex preform has a geometry to cause alengthening of fabric fibers when applied. In an embodiment, the bladeportion is more pronounced or bigger toward the center 704 than towardthe end 706 of the blade portion. That is, the blade portion is shapedto cause the fibers of the preform fabric to be longer to traverse thedistance towards the more pronounced center of the blade than around theends of the blade. As discussed above, the geometry of the blade portionwould be opposite for a concave preform so that the fibers of thepreform fabric will be shorter to traverse a distance towards a lesspronounced center of the blade than around the ends of the blade.

A force F is applied to urge the upper and lower clamps together. Asshown in FIG. 7B, the distance 702 is narrowed so blade portion 608enters into the gap 612 in the lower clamp. Distance 702 is adjusted asnecessary to enable passage of the preform fabric around the bladeportion and intersection of the upper and lower clamps. The bladeportion 608 causes the fibers of the preform fabric to be longer totraverse the distance towards the more pronounced center of the blade704 than around the ends of the blade.

While FIG. 2 illustrates an example that results in a fabric with asingle curvature, it is possible to design a variety of clamp sets toachieve more complex geometries. For example, an oval shaped preform canbe created by varying the amplitude of the clamp curvatures along thelength of the preform. In FIG. 9, an example of an O preform 900 isshown that was made in accordance with the instant invention. It iscontemplated that clamp pairs may be applied to some portions of thepreform fabric and not to other portions. That is, additional fiberlength may be pulled from the loom in some areas of the preform fabricand not in other areas of the preform fabric. In this way, complexgeometries of preforms with curved and straight portions can be formed.Some examples of such complex shaped preforms are illustrated in FIG. 8.

Once the required fabric length is woven and the preform fabric isremoved from the loom, any remaining clamps can be removed and thepreform fabric shaped to the final configuration. In any of theembodiments, the final configuration can be impregnated with a matrixmaterial. The matrix material includes epoxy, bismaleimide, polyester,vinyl-ester, ceramic, carbon, and other such materials known to those ofordinary skill in the art.

Other embodiments are within the scope of the following claims.

The invention claimed is:
 1. A method of forming a curved preformcomprising: applying at least one set of mating clamps to fibers of apreform fabric advancing from a loom, the at least one pair of matingclamps capturing at least a portion of the preform fabric there between,the at least one set of clamps having a geometry including a first fiberpath and a second fiber path, wherein the first fiber path is longerthan the second fiber path, thereby causing an increase in a length offibers traversing the first fiber path by pulling at least some of thefibers advancing from the loom; and shaping the preform into a curve,wherein the fibers are continuous along a length of the preform fabric.2. The method of claim 1, wherein there are at least two sets of matingclamps applied to the preform fabric, the mating clamps configured toreceive a fabric therebetween.
 3. The method according to claim 1,comprising: applying a force to each set of mating clamps to compressthe preform fabric there between.
 4. The method according to claim 1,wherein the increase in length of the fibers is in the warp direction.5. The method according to claim 2, comprising: disposing the at leasttwo sets of mating clamps adjacent one another; and joining the at leasttwo sets of mating clamps to one another.
 6. The method according toclaim 2, comprising: arranging the two or more sets of mating clamps inseparate locations of the fabric to increase the length of warpdirection fibers in each of the separate locations but not in otherlocations.
 7. The method of claim 1, wherein each set of mating clampsincludes an upper clamp portion and a lower clamp portion.
 8. The methodof claim 7, wherein the lower clamp portion is two mating parts.
 9. Themethod of claim 1, wherein the length of the fibers is greater at anoutside of the curve than at an inside of the curve.
 10. The method ofclaim 1, wherein the first fiber path is undulated.
 11. The method ofclaim 10, wherein the second fiber path is straight.